August 11, 2005

When Does Good Food Go Bad?

True or false: You can leave coffee in the pot and drink it the next day.

True. Coffee will eventually grow surface mold but usually not in one day, says Donald W. Schaffner, extension specialist in food science and professor at Rutgers.

It's drinkable, but it won't taste as fresh because the compounds that form coffee's characteristic aroma and flavor evaporate at room temperature, says Purnendu C. Vasavada, professor of food science and microbiology at the University of Wisconsin-River Falls. Refrigerating helps coffee keep its flavor fresher the next day.

False. Well, it's partially true. Europeans traditionally don't refrigerate eggs, and we didn't always have mandatory refrigeration. "However, the United States now requires refrigeration because we know that salmonella can sometimes [very rarely -- 1 in 10,000 or 20,000 eggs] be present. If the eggs were not refrigerated, salmonella would be able to multiply to very high levels [in those rare eggs]," says Schaffner.

Eggs last about three to five weeks in the fridge, as long as you purchase them before the expiration date. But don't store them in the door, advises Meredith H. Luce, a clinical dietitian at Florida Hospital in Orlando. Store eggs in their cartons in the center or back of the fridge, where the temperature fluctuates less than near the door.

True or false: Keeping bread in the refrigerator prevents it from going stale.

False. Bread actually gets stale faster in the fridge. However, if it's hot and humid in your house, refrigeration retards mold growth. According to Schaffner, "Bread goes stale because of changes to the starch molecules. As bread bakes, the heat of cooking changes the starch molecules so that they can absorb water. Once the bread is baked, the starch starts to lose moisture, and the starch molecules toughen up -- this is staling."

If you need to keep bread longer, freeze it.

True or false: Pizza left out overnight is perfectly safe.

True AND false. From a taste perspective, it's just fine. However, "From a public health perspective, you shouldn't eat pizza left out for more than a few hours -- it could potentially be hazardous," says Schaffner. On the other hand, not too many people have become sick from eating pizza that was left out all night. When pizza comes out of the oven, almost all the pathogens are inactive. And between the acidic tomato sauce (not hospitable to bacteria) and the pasteurized cheese, as well as the fact that all cheese was designed to last without refrigeration, it's probably safe from a practical standpoint. However, Schaffner cautions that if the pizza has sausage, pepperoni or other meat, the risk increases -- he suggests tossing it.

True or false: Eating black or brown spots on bananas is perfectly fine.

True. I always thought the black parts were unsafe, but it's OK if you like the way they taste. "The color change is due to biochemical changes in the fruit, not to the presence of harmful bacteria," says Schaffner.

The best place to store bananas is outside the refrigerator, unless you want to stop the ripening process, in which case the coolness of the fridge will do this, but it'll also darken the peel (not the edible part).

True or false: You can refreeze meat, poultry and other foods once they've been defrosted.

True. Once frozen food is thawed in the refrigerator, it is safe to refreeze without cooking, although there may be a loss of quality due to moisture loss. Also, after cooking raw foods that were previously frozen, it is safe to freeze them. If cooked foods are frozen and then thawed in the refrigerator, you may refreeze the unused portion.

Repeated freezing and thawing can affect the texture, so the quality may suffer. But as long as food is thawed properly (so pathogens don't multiply to dangerous levels), it is an acceptable practice, says Schaffner. However, if you refreeze foods that were left out or thawed incorrectly and have grown bacteria, you will be refreezing a dangerous food, cautions Keith R. Schneider, a professor of food science at the University of Florida in Gainesville.

True or false: Freezer burn is caused by dangerous pathogens, and the food should be discarded immediately.

False. Freezer-burned food is perfectly safe. It just won't taste very good because it may be tough and dried out, says Schaffner. Freezer burn results from trapped air that causes moisture crystals to form around the food and change it physically. "Any alteration in the physical properties of a food will affect the taste. We've all witnessed how cooking a food changes it. Cut freezer-burned portions away either before or after cooking the food. Heavily freezer- burned foods may have to be discarded," adds Luce.

Freezer burn can be prevented by wrapping food tightly in a moisture-proof barrier (e.g., plastic wrap or a sealed bag). Wrapping it in multiple layers can also help. Foods left in the freezer too long (even when well-wrapped) will suffer freezer burn, so wrap and date all packages, and use the oldest packages first, suggests Schaffner.